The Israeli Journal of Aquaculture - Bamidgeh, IJA_65.2013.917, 8 pages
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Feed Requirements for Maintenance and Growth of
Anemone Clownfish Amphiprion percula
I. Lupatsch1*, R.J. Floyd1, R.J. Shields1, D.L. Snellgrove2
1
Centre for Sustainable Aquaculture Research, Swansea University,
Swansea, UK
2
WALTHAM Centre for Pet Nutrition, Waltham-on-the Wolds, Melton
Mowbray, Leicestershire, UK
(Received 17.10.12, Accepted 29.11.12)
Key words: energy metabolism, protein efficiency, ornamental fish,
maintenance requirement
Abstract
Daily energy and protein requirements of the anemone clownfish, Amphiprion
percula, were determined as the sum of requirements for maintenance and
growth according to the following approach: requirement = a  W(kg)b + c 
gain. The daily weight gain (mg) at 27°C was described as a function of body
weight (g): y = 5.39 × W(g)0.284. Utilization efficiencies of gross energy and
crude protein for maintenance and growth were determined by feeding two
groups of fish (initially 0.2 g and 1.3 g, 27°C) at increasing levels from
maintenance to apparent satiation. The energy and protein contents of the
whole body averaged 5.39 kJ and 140 mg per g body mass, respectively.
Weight gain in relation to feed intake was plotted and the slopes of the
resulting linear relationships describe the utilization efficiencies of dietary
energy and protein for growth. For maintenance, or zero growth, the daily
requirement of gross energy was GEmaint = 43.2 kJ/kg0.80 and for crude protein
CPmaint = 0.43 g/kg0.70. To deposit one g of weight gain, inputs of 35.7 kJ
gross energy and 0.72 g crude protein were required.
*Corresponding author. E-mail: [email protected]
2
Lupatsch et al.
Introduction
Between 1.5 and 2 million households worldwide are believed to keep tropical marine
aquaria and the collection trade which supplies this industry is estimated at US$220-330
million annually (Wabnitz et al., 2003). The majority of these imports are destined for
the United States, Europe, and Japan (Chapman et al., 1997). Unlike freshwater aquaria
species, where 90% of fish species are farmed, only 100 of the 800 species traded in the
marine ornamental industry are captive-bred. The family Pomacentridae, particularly
clownfish species of the genus Amphiprion, represents the most important group of
captive-bred marine species. Among all species, Amphiprion sp. is the best known to
aquarium traders due to its color pattern, interesting behavior, and robustness. From
1997 to 2002, A. ocellaris was the most common species of marine ornamental fish and
made up 15.6% of the total number exported worldwide and over 25% into European
countries (Wabnitz et al., 2003).
One of the major drivers of growth in the fish-keeping hobby over the last 50 years is
the development of commercially available manufactured feed. The acceptance and
reliance of the mainstream hobby on manufactured feeds has turned attention to the
need to quantify the nutritional requirements of these fish (Sales and Janssens, 2003).
The quality of feeds is not only an issue in the day-to-day husbandry of these animals
but also in their large scale production. With the intensification of modern ornamental
fish production, a supply of nutritionally-balanced and affordable feeds is required. The
aquarium industry is relatively small despite its very high value, thus few studies on the
nutritional requirements of ornamental fish have been published (Priestley et al.,
2006a,b,c). A main problem within the trade is the diversity of fish kept in home aquaria,
each with its own nutritional requirements.
Nutrient requirements have often been quantified by dose-response relationships
(Elangovan and Shim, 1997; Kruger et al., 2001; Ling et al., 2006) but this approach is
time consuming and limited in application. In the following study, an attempt was made
to apply a factorial approach for determining feed requirements for ornamental fish such
as A. percula. The method itself was successfully applied to determine requirements in
farmed fish (Lupatsch et al., 2001; 2003a,b; Lupatsch and Kissil, 2005). The advantage
over the more traditional empirical based dose-response methods is that it can be used
to describe protein and energy requirements for growing fish throughout the production
cycle. Estimations are not necessarily restricted to within the size range of the test
species and, so, are applicable to a broad range of fish. Key to achieving this however is
establishing the utilization efficiencies and maintenance requirements for protein and
energy, an assessment of the whole body composition as a function of fish size, and
growth potential of the target species under a given set of culture conditions.
Materials and Methods
Methodology. The premise behind the factorial method is that the requirements for
protein and energy can be partitioned into growth and maintenance costs based on the
assumption that the two are additive. The requirement for maintenance at a constant
temperature is primarily dependent upon body size and proportional to the metabolic
body weight in the form of a × W(kg)b, where a is a constant, characteristic of a certain
fish species at a set temperature and b is the exponent of the metabolic weight which, in
fish, has been determined as b = 0.80 and b = 0.70 for energy and protein, respectively
(Lupatsch et al., 2003b; Lupatsch, 2009). The requirement for growth on the other hand
is dependent upon the amount and composition of the weight gain. This can be
expressed as: energy needs (kJ/day/fish) = a × body weight (kg) 0.80 + c × energy gain
(kJ), where a × (kg)0.80 = maintenance requirement and c = cost in units of dietary
energy to deposit energy as growth. The same approach is used to quantify protein,
except for the use of exponent b = 0.70 for metabolic body weight. Protein needs
(g/day/fish) = a × body weight (kg)0.70 + c × protein gain (g), where c = cost in units of
dietary protein to deposit protein as growth. The significance of this approach is that
protein and energy needs are expressed primarily in terms of absolute demand per fish
body mass and anticipated weight gain, and only secondarily as a percentage of the feed.
Feed requirements of clown fish
3
Fish and rearing conditions. Amphiprion percula juveniles were spawned from
breeding pairs obtained from the wild, housed in the Centre for Sustainable Aquaculture
Research (CSAR), and raised in the recirculation system under controlled conditions.
Water temperature was maintained at 27.0°C±0.8 (mean±SD) and salinity was 32.0±0.7
ppt. The light regime of the room was kept at 16L:8D. Fry were separated from the
adults after hatching, initially reared on enriched rotifers and Artemia, and after 15 days
post-hatch progressively weaned onto a formulated larval feed (52% protein, 12% lipid).
Growth prediction and composition of weight gain. This section describes the methods
for historic data obtained by CSAR for clownfish growth prediction and composition of
weight gain. The data were utilized to estimate feed requirements described in this
current study. To be able to achieve this, the growth potential of clownfish growth was
monitored for several batches of fish from 15 days post-hatch (i.e., after the live feed
stage) to about 2.5 g. Depending on size, groups of clownfish were kept in 20-l tanks
and fed commercially available feeds to supply 52-45% dietary protein and 12% lipid to
apparent satiation three times per day. Fish were bulk weighed every 10 to 14 days, and
the average daily weight gain during two successive weighings was calculated. The
corresponding body weight for the period was the geometric weight of the fish during the
weighing period. Thus a data set of n = 29 referring daily weight gain to fish weight at a
temperature of 27°C was obtained. In addition, 5 groups of 5-10 equal sized fish
representing different weight classes were sampled along this growth period to be
analyzed for whole body composition.
Requirement for maintenance. To quantify the requirements of energy and protein for
maintenance of A. percula, two growth trials were performed with fish weighing 0.2 g
and 1.3 g initially. The experimental system consisted of 12 identical 20-l glass aquaria.
The tanks were covered with individual mesh covers to prevent the fish from escaping.
Stocking density was 25 fish per aquarium in Trial 1 and 15 fish per aquarium in Trial 2.
In each trial, triplicate groups of fish were fed manually at increasing amounts from low
to apparent satiation, referred to as maintenance, low, medium, and high (supplied at
decreasing levels of apparent satiation). Feed was fed three times a day at the satiation
level, decreasing to once daily at the low feeding level to ensure equal distribution of the
flakes among the fish. The feed was based on the Aquarian® Marine (closed formula),
prepared as dry flakes by MARS Fishcare® and supplied by the WALTHAM® Centre for Pet
Nutrition (Leicestershire, UK). The main ingredients include fish and fish derivatives,
mollusks and crustaceans, cereals, oils and fats, algae, minerals, and vitamins.
Proximate composition of the feed as analyzed was 925 mg dry matter, 394 mg crude
protein, 110 mg lipid, and 132 mg ash/g as fed; gross energy was 18.63 kJ/g as fed.
Chemical analyses. Identical analyses were applied for feeds and body homogenates.
Dry matter was calculated by weight loss after 24 h drying at 105°C in the oven. Ash was
calculated from the weight loss after incineration of the samples for 12 h at 550°C in a
muffle furnace. Crude protein was measured using the Kjeldahl technique and multiplying
nitrogen by 6.25. Crude lipid was determined after chloroform-methanol extraction.
Samples were homogenized with a high speed homogenizer for 5 min and lipid was
determined gravimetrically after separation and vacuum drying (Folch et al., 1957).
Gross energy content was measured by combustion in a Parr bomb calorimeter (Model
6200) using benzoic acid as the standard.
Definitions and statistical procedures. Specific growth rate (SGR) = 100(Ln final BW Ln initial BW)/time in days, where BW = body weight in g. Feed conversion ratio (FCR) =
feed intake/live wt gain. Feed intake (%/BW/day) = 100(daily feed intake/geometric
mean wt), where geometric mean = (initial BW  final BW)0.5.
Linear and non-linear equations were obtained by regression analysis and optimal
parameter estimates were obtained with the iterative non-linear least squares algorithm
of Levenberg-Marquardt. All statistical analyses were carried out using SigmaPlot 8.0
(SPSS Inc., Chicago, IL, USA). For enhanced clarity the performance parameters in
Tables 1 and 2 are presented as average values per treatment (means±SD), whereas all
data points in the graphs were used to establish the linear equations.
4
Lupatsch et al.
Results
Requirements for maintenance. Weight gain, feed intake, and FCR observed in Trials 1
and 2 are shown in Table 1. As expected, when fed at the highest level, feed intake and
specific growth rate were higher in smaller than in larger fish. On the other hand, to
satisfy minimum maintenance requirements or to prevent negative growth, the smaller
fish needed to consume 1.5% per day per body mass whereas the larger fish needed
only 0.80%.
Table 1. Growth performance of Amphiprion percula fed increasing feed levels (mean±SD of
triplicate treatments).
Initial wt
(g/fish)
Trial 1 – 41 days
Maintenance
Low
Medium
High
Trial 2 – 28 days
Maintenance
Low
Medium
High
Final wt
(g/fish)
SGR
Feed intake
(%/body wt/day)
FCR
Survival
(%)
0.217±0.015
0.215±0.015
0.221±0.012
0.227±0.019
0.185±0.016
0.256±0.017
0.328±0.035
0.367±0.021
-0.39±0.06
0.43±0.13
0.96±0.13
1.18±0.07
0.93±0.02
1.95±0.04
3.00±0.32
3.51±0.14
4.87±1.72
3.14±0.35
2.96±0.28
100.0±0.0
100.0±0.0
90.7±12.8
98.7±4.6
1.30±0.15
1.33±0.10
1.32±0.02
1.36±0.09
1.24±0.12
1.33±0.09
1.41±0.06
1.54±0.10
-0.16±0.13
0.00±0.0
0.22±0.16
0.44±0.18
0.51±0.22
0.76±0.12
1.18±0.40
1.63±0.30
6.52±2.79
3.87±0.75
82.2±20.4
91.1±3.8
84.4±10.2
80.0±17.6
Wt gain (mg/fish/day)
To further examine the feed requirements of clownfish, the relationship between feed
intake and weight gain for each trial is illustrated in Fig. 1. The more feed was consumed,
the higher was the weight gain. The relationship between x = feed fed (mg) and y =
weight gain (mg) per day per fish can be described by linear equations as y =
-1.45±0.23 + 0.49±0.03x, r2 = 0.96 for Trial 1 and y = -5.18±0.50 + 0.50±0.03x, r2 =
0.96 for Trial 2. According to these equations,
the maintenance requirement (zero growth) of
the 0.2 g fish would amount to approximately
3.0 mg feed per day per fish and 1.3 g fish
would require 10.4 mg feed per day.
As the energy and protein content of the
feed is known, relationships between energy
intake and protein intake versus weight gain
can be established. In addition, to be able to
combine both fish sizes, we used metabolic
body weights for energy (kg0.80) and protein
(kg0.70) determined for other fin fish (Lupatsch
et al., 2001; 2003a; Lupatsch and Kissil, 2005).
By expressing gross energy intake (x) and the
subsequent weight gain (y) per unit of
Feed fed (mg/fish/day)
metabolic body weight (kg0.80), the combined
Fig.
1.
Relationship
between daily feed
results of the two trials are described by the
intake
(mg)
and
weight
gain (mg) of the
following linear equation: y = -1.21±0.11 +
2
clownfish,
Amphiprion
percula,
with initial
0.028±0.001x, r = 0.95 (Fig. 2). From this
weights of 0.2 g and 1.3 g.
equation and Fig. 2, it can be concluded that
the daily requirement for energy at zero growth
(y = 0) is approximately 43.2 kJ/kg0.80. The efficiency of dietary energy to deposit growth
above maintenance is 0.028, meaning 35.7 kJ (1/0.028) are needed to deposit one g of
weight gain.
In parallel, the relationship between crude protein fed (x) and weight gained (y), both
expressed per unit of metabolic weight (kg0.70), is presented and described by the
following equation: protein: y = -0.60±0.04 + 1.38±0.06x, r2 = 0.96 (Fig. 3). From this
Feed requirements of clown fish
5
Wt gain (g/kg0.80/day)
Wt gain (g/kg0.70/day)
equation, the daily crude protein needed for maintenance was estimated at 0.43g kg0.70.
Here the efficiency of dietary protein to deposit growth above maintenance is 1.38,
meaning 0.72 g (1/1.38) are needed to deposit one g of weight gain.
Crude protein fed (g/kg0.70/day)
Gross energy (kJ/kg0.80/day)
Fig. 2. Daily weight gain of Amphiprion percula
Fig. 3. Daily weight gain of Amphiprion
fed increasing levels of energy expressed per percula fed increasing levels of crude protein
metabolic body weight of kg0.80 for fish of 0.2 g expressed per metabolic body weight of kg0.70
and 1.3 g combined.
for fish of 0.2 g and 1.3 g combined.
Table 2. Whole body content of Amphiprion
percula (per g wet weight) at increasing sizes
(historic data set at CSAR).
Moisture (mg)
Protein (mg)
Lipid (mg)
Ash (mg)
Energy (kJ)
0.16
767
133
32.6
53.4
4.63
Body weight (g)
0.35
0.40
0.60
752
739
716
134
139
141
29.8
44.5
53.9
62.3
56.0
62.1
4.52
5.27
5.58
1.20
697
150
75.7
51.1
6.93
Wt gain (mg/fish/day)
Requirements for growth. The daily weight gain of A. percula at different body sizes is
depicted in Fig. 4. In studies with several fish species the best curve fit to describe the
daily weight gain (y) dependent on fish weight was obtained using the following common
equation: y = a  BW (g)b (Lupatsch et al., 2003b). In similar fashion, the average daily
weight gain (n = 29) of clownfish at a temperature of 27°C can be described as follows:
y = 5.39±0.16  BW(g)0.284±0.027, r2 = 0.89, where y = weight gain in mg/fish/day and
BW = body weight in g/fish for sizes from 0.02 to 2.4 g. Rearranging this equation, the
body weight BWt can be predicted from the initial body weight BW0 after t days as BWt =
(BW0 0.716 + 0.00386  t) 1.397.
To estimate the energy and protein content of a unit of weight gain, the body
composition at selected fish sizes is presented
in Table 2. A slight increase in lipid and energy
content can be observed in concurrence with
decreasing moisture content relative to fish
size, whereas protein and ash content stay
relatively constant.
Fish wt (g)
Fig. 4. Daily weight gain (mg) of
Amphiprion percula at increasing weights.
6
Lupatsch et al.
Discussion
A parallel can be drawn with commercial culture of food fish as aquaculture is utilizing an
increasing variety of fish that show differences with respect to feed requirements and
conversion efficiencies.
Growth and composition of weight gain. Some of the differences in feed requirements
and conversion efficiencies are due to the growth potential and composition of growth.
We assume that fish have a genetically determined asymptotic body size and composition
of weight gain, and that the maximum obtainable body size for most ornamental fish is
far smaller than for fish grown for human consumption. The growth model set up in the
present study (Fig. 4) does not cover the whole life cycle of anemone clownfish and a
larger dataset might enhance the prediction. However, it does agree favorably with a
number of studies such as Gordon et al. (1998) who carried out several trials raising A.
percula larvae post hatch to a size of 0.3 g. It corresponds as well with another study
with clownfish (Johnston et al., 2003) that covered the size range between 0.08 g and
0.35 g. According to our equation for predicting growth, A. percula might reach a size of
1.6 g after one year and 4.3 g in 2 years, or at least until the phase where dimorphism
sets in as females are dominant and usually grow larger than males. To our knowledge
growth has not been monitored for the whole life cycle, however the average size and
weight of an adult A. percula is about 60 mm and 10 g respectively; they can typically
live to 8-10 years and in extreme cases up to 30 years (Buston and Garcia, 2007).
Because a large proportion of energy and protein consumed by fish is retained as
growth, the composition of the gain is an additional factor determining energy and
protein requirements. Like other fish, A. percula show a tendency to increase energy
density with size or age (Table 2) though whole body protein content is rather constant
(Lupatsch et al., 2003b). However, due to a limited data set and for immediate
application of estimating feed requirements, an average energy content of 5.39 kJ and
protein content of 140 mg per g body mass might be assumed.
Maintenance requirements. Metabolic body weight describes the rate of energy
expenditure relative to fish size. As the exponent b for the metabolic body weight for
energy and protein have not been determined for A. percula, exponents of b = 0.80 and
0.70, respectively, were used. The exponents for the metabolic weights are quite similar
for various fish species as described in Lupatsch (2009), so it is not unreasonable to
accept them for A. percula as well. Thus metabolic weight, as opposed to absolute
weight, enables us to establish the maintenance requirements of A. percula at different
sizes (Figs. 2 and 3), resulting in GEmaint = 43.2 kJ/kg0.80. Johnston et al. (2003)
suggested that feeding 0.1 g clownfish 2% of their body mass would supply the
requirements just above maintenance. Conversion of their data set reveals that this
amounts to GE = 58 kJ/kg0.80, at which level clownfish still show positive growth.
Pannevis and Earle (1994) assessed the maintenance energy requirements of several
ornamental species by using the same method of examining the relationship between
growth rate and energy intake. Recalculation of their data established that the average
daily maintenance requirements for goldfish were GEmaint = 19.2 kJ/kg0.80 and CPmaint =
0.20 g/kg0.70 whereas for neon tetra they amounted to GEmaint = 66.2 kJ/kg0.80 and CPmaint
= 0.55 g/kg0.70. Maintenance requirements for goldfish appear to be rather low but
possibly reflect the fact that the trials were carried out at a temperature of 20°C whereas
for other ornamental species 26°C was used.
Taking into consideration the effect of temperature, energy maintenance
requirements of clownfish show similar values to those found for food fish. In a study by
Huisman (1976), the daily maintenance requirement was estimated at 66 kJ DE/kg0.80
for carp, Cyprinus carpio, and and 48 kJ DE/kg0.80 for rainbow trout, Oncorhynchus
mykiss, at 23°C and 15°C, respectively. Depending on temperature, the maintenance
requirement of gilthead sea bream, Sparus aurata, increased from 46.3 kJ DE/kg0.80 at
21°C to 77.0 kJ DE/kg0.80 at 28°C (Lupatsch et al., 2003a). It is quite striking how close
these values are among fish species; on the other hand the difference compared to
homoeothermic vertebrates is remarkable, as their energy requirements for basal
metabolism are up to 10-fold higher, averaging 300 kJ/kg0.75 per day (Kleiber, 1965).
Feed requirements of clown fish
7
Protein and energy utilization efficiency. Determining the efficiency of gross energy to
deposit growth was done by linear regression of weight gain against gross energy intake
when both are expressed per metabolic body weight of kg 0.80. Using the slope of 0.028 of
the linear equation relating weight gain to energy intake, it can be concluded that 35.7 kJ
(1/0.028) of gross energy are needed to deposit one g of weight gain. According to Table
2, the average energy content of 5.39 kJ per g gain was determined. Thus the partial
efficiency of energy gain versus gross energy fed is 5.39/35.7 = 0.15. The same
calculation can be done for protein. In this case 0.72 g (1/1.38) of crude protein is
needed to deposit one g of weight gain. Protein content per g gain is around 140 mg
(Table 2). Therefore the partial efficiency of protein gain versus crude protein fed is
0.14/0.72 = 0.19.
The efficiency of energy utilization (i.e., the slope of energy gain as a function of
energy intake) for clownfish compared to food fish is rather low. Values range between
efficiencies of 0.65, 0.68, and 0.69 for gilthead sea bream, European sea bass, and white
grouper, respectively (Lupatsch et al., 2003b). One of the explanations might be that, in
the last three species, efficiencies are expressed in units of digestible energy rather than
gross energy as done for clownfish. In addition, during the growth trials, whole body
composition was analyzed for the food fish, resulting in a more precise assessment.
Further, clownfish are slow feeders and despite careful monitoring of feed intake, feed
losses might have occurred as a result of leaching and break-up of flakes.
Implications for feed formulation. Using the approach described above, daily
requirements for energy and protein in growing A. percula can be calculated for a specific
body weight and at any level of growth. The absolute daily energy and protein
requirement of clownfish (Table 3) is dependent upon size and anticipated weight gain.
The proportion of total dietary energy required for maintenance increases with increasing
body weight and decreasing growth rate, influencing the feed conversion ratio. The
Table 3. Daily energy and protein requirements of anemone clownfish Amphiprion percula
at 27°C.
Predicted wt gain (mg/day)1
Energy requirement (J/fish/day)
Gross energy required for maintenance2
Expected energy gain3
Gross energy required for growth4
Gross energy required for maintenance and growth
Protein requirement (mg/fish/day)
Crude protein required for maintenance5
Protein gain6
Crude protein required for growth7
Crude protein required for maintenance and growth
Feed formulation
Gross energy content of feed (kJ/g)
Required feed (mg/fish/day)8
Required feed (%/body wt/day)
Feed conversion ratio
Crude protein content of feed (mg/g)9
Crude protein to gross energy ratio (mg/kJ)
1
0.15
3.1
Body wt (g)
0.75
5.0
3.00
7.4
38
17
114
151
137
27
179
316
414
40
266
680
0.9
0.44
2.3
3.2
2.8
0.70
3.7
6.5
7.4
1.03
5.5
12.8
18
8.4
5.6
2.67
385
21.4
18
17.6
2.3
3.53
369
20.5
18
37.8
1.3
5.13
340
18.9
according to y = 5.39 x BW(g)0.284, where y = weight gain in mg and x = feed fed in mg
according to 43.2 kJ/kg0.80
3
weight gain  energy content of gain (5.39 kJ/g)
4
expected energy gain × 6.7 (1/0.15), i.e., cost in units of GE to deposit one unit of energy as growth
5
according to 0.43 g/kg0.70
6
expected protein gain = weight gain  protein content of gain (140 mg/g)
7
expected protein gain  5.3 (1/0.19), i.e., cost in units of CP to deposit one unit of protein as growth
8
required feed intake to meet daily energy requirements while using a feed containing 18 GE kJ/g
9
required dietary protein level to meet daily protein requirements
2
8
Lupatsch et al.
dietary protein to energy ratio also decreases with increasing fish size and decreasing
growth potential. Thus small clownfish of 0.15 g should be fed a 40% protein feed,
whereas gradually reducing to a 35% protein feed would suffice for larger fish up to 3 g.
When looking at studies with other ornamentals, the optimal dietary protein content
appears quite variable among species. It is difficult to say whether this variation is simply
due to methodological differences or the result of real species-specific differences.
According to Lochmann and Phillips (1994) protein requirements of goldfish were
established at 29% dietary inclusion, whereas Fiogbé and Kestemont (1995) observed
that goldfish larvae required 53% crude protein. Studies with the tin foil barb,
Barbonymus schwanenfeldii (Elangovan and Shim, 1997) and the swordtail, Xiphophorus
hellerii (Kruger et al., 2001) reported protein requirements of 41% and 45% crude
protein, respectively. Research carried out by Sealey et al. (2009) indicated that neon
tetras of 0.18 g grew best when diets contained at least 45% crude protein whereas
Chong et al. (2000) found the optimal dietary protein level to be 45-50% for the discus,
Symphysodon aequifasciata. Royes et al. (2006) compared the effects of two protein and
lipid levels on growth of two juvenile African cichlids, Pseudotropheus socolofi which is
considered to be omnivorous and Haplochromis ahli to be more carnivorous, and
hypothesized that the omnivore would have a lower protein requirement than the
carnivorous one. The results were inconclusive since no differences were found whether
feeding the carnivorous cichlid a 55% protein or a 35% protein feed, whereas the
omnivorous fish did better with the high protein/high lipid feed.
One of the factors affecting the optimal dietary protein content may well be the use of
fish of different weights, as dietary protein requirements decrease with increasing fish
size. A further difference between studies is the choice of feeding rate which could vary
from a given proportion of biomass to ad libitum feeding. Therefore, expressing
requirements only in terms of a percentage of the diet can be misleading, if the feed
intake is not considered. This concept has been confirmed for food fish (Lupatsch, 2009)
so the general biological principle should be relevant here as well.
In conclusion, energy and protein requirements of ornamental fish are dependent
upon growth potential, composition of weight gain, and demand for maintenance,
regardless of whether they are carnivorous or herbivorous, marine or freshwater fish. For
pet feed producers this means that they have to formulate a specific feed in combination
with a suitable feeding regime. This could be adapted firstly under commercial farming
conditions that concentrate on maximum growth rate, and thereafter in public or home
aquaria environments where fish are kept for display rather than fast growth.
References
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America trade in ornamental fish. J. World Aquacult. Soc., 28:1-10.
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